ER1: Electricity

1. Using the chart shown below, rank the top four sources of electrical energy in the US.
2. Based on the reading accompanying ER1: Electricity, which household appliance is most like a "steam turbine"?

• A: Clothes iron, because it uses steam
• B: Knife, because it has a blade
• C: Fan, because it rotates
• D: Battery charger, because it transforms electricity

3. Consider the waterwheel shown in the picture to the above-right. Based on the reading accompanying this exercise, do you think this is the most common way of turning hydropower into electricity? What did you read to support your conclusion?

Click to Enlarge

---

The diagram above shows the flow of electrical energy, from its source on the left, to the sector that uses it on the right. The thickness of the arrows is proportional to the quantity of energy, so it the larger amounts of energy can be identified without relying on the numbers that accompany the chart.

Electricity in the United States

Most of the electricity in the United States is produced using steam turbines.

A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. In a steam turbine, steam is forced against a series of blades mounted on a shaft, thus rotating the shaft connected to the generator. The generator, in turn, converts its mechanical energy to electrical energy based on the relationship between magnetism and electricity.

In steam turbines powered by fossil fuels, such as coal, petroleum (oil), and natural gas, the fuel is burned in a furnace to heat water in a boiler to produce steam.

Fossil Fuels Generate Most U.S. Power

In 2011, coal was the fuel for about 42% of the 4 trillion killowatthours of electricity generated in the United States.

Nuclear Power Provides About One-Fifth of U.S. Electricity

Nuclear power is a method in which steam is produced by heating water through a process called nuclear fission. In a nuclear power plant, a reactor contains a core of nuclear fuel, primarily uranium. When atoms of uranium fuel are hit by neutrons, they fission (split) releasing heat and more neutrons. Under controlled conditions, these other neutrons can strike more uranium atoms, splitting more atoms, and so on. Thereby, continuous fission can take place, creating a chain reaction releasing heat. The heat is used to turn water into steam, that, in turn, spins a turbine that generates electricity. Nuclear power was used to generate about 19% of all the Country's electricity in 2011.

Renewable Energy Sources Make Up the Rest

Hydropower, the source for 8% of U.S. electricity generation in 2011, is a process in which flowing water is used to spin a turbine connected to a generator. There are two basic types of hydroelectric systems that produce electricity. In the first system, flowing water accumulates in reservoirs created by dams. The water falls through a pipe called a penstock and applies pressure against the turbine blades to drive the generator to produce electricity.

In the second system, called run-of-river, water is diverted from a river using a relatively low dam or weir into penstocks and turbines. The dam does not store a large volume of water in a reservoir. Run-of-river power plants are more dependent on river flows than hydro plants with reservoirs for storing water which can produce electricity even when natural river flows are low.

• Source: http://www.eia.gov/energyexplained/index.cfm?page=electricity_in_the_united_states